A Guide to Audio-Frequency Induction wbr Loop Systems

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					A Guide to Audio-Frequency
    Induction Loop Systems
Contents

About this guide .................................................................................................................. 3
What is an audio frequency induction loop system? ...................................................... 4
How does an induction loop system work? .................................................................... 5
Why we have induction loop systems .............................................................................. 6
Where are ‘aids to communication’ required? ................................................................ 7
Which induction loop system should I use? .................................................................. 9
     1.2m2 PL1 Portable Induction Loop System .................................................................................... 10
     1.2m2 ML1/K Counter Induction Loop System ................................................................................ 11
     1.2m2 PDA102C Counter Induction Loop System .......................................................................... 12
     1.2m2 VL1 Vehicle Induction Loop System ......................................................................................13
     50m2 PDA102L/R/S Small Room Induction Loop System .............................................................. 14
     50m2 DL50/K Domestic Induction Loop System ..............................................................................15
     120m2 ‘AK’ Range Induction Loop Kits / PDA200E Amplifier............................................................16
     200m2 PDA200/2 Professional Induction Loop Amplifier ..................................................................17
     500m2 PDA500/2 Professional Induction Loop Amplifier ..................................................................17
     900m2 PDA1000/2 Professional Induction Loop Amplifier .............................................................. 17
     Microphones .................................................................................................................................... 18
     Outreach Plates ................................................................................................................................19
     Induction loop cable ........................................................................................................................ 21

Induction loop system design and installation ............................................................ 22
     Maximum area coverage.................................................................................................................. 22
     Loop amplifier position .................................................................................................................... 22
     Loop cable position .......................................................................................................................... 22
     Dead spots ...................................................................................................................................... 23
     Overspill............................................................................................................................................ 23
     ‘Low overspill’ reduced sized loops .................................................................................................. 24
     ‘Low overspill’ phase shifting loops .................................................................................................. 24
     ‘Low overspill’ fixed table loops ........................................................................................................ 25
     Mains hum........................................................................................................................................ 25
     Interference ...................................................................................................................................... 25
     Damage to the loop.......................................................................................................................... 26
     The ‘isolation’ issue .......................................................................................................................... 26
     Vertical loops .................................................................................................................................... 26
     In summary ...................................................................................................................................... 26

Testing an induction loop system .................................................................................. 27
PDA range part numbers .................................................................................................. 29




                               A GUIDE TO AUDIO-FREQUENCY INDUCTION LOOP SYSTEMS • PAGE 2
About this guide
Induction loop systems are more properly termed AFILS, which stands for audio-frequency
induction loop systems.

This guide - brought to you by the manufacturers of the PDA range of audio-frequency
induction loop systems - aims to provide straightforward explanations of the technology
involved together with hints, tips and advice on best practice installation.

In the UK, the installation of induction loop systems is governed by BS7594 (The Code of
Practice for Audio-Frequency Induction Loop Systems) and EN60118-4 (Magnetic field
strength in audio frequency induction loop systems for hearing aid purposes), copies of
which are available from the British Standards Institute, 389 Chiswick High Road, London
W4 4AL. Tel: +44 (0)20 8996 9000. Web: www.bsi-global.com.

Other National standards of design, installation and commissioning should be referenced
where pertinent.




                  A GUIDE TO AUDIO-FREQUENCY INDUCTION LOOP SYSTEMS • PAGE 3
What is an audio-frequency induction loop system?
Audio-frequency induction loop systems allow hearing impaired people to hear more clearly.
Most hearing aids have a ‘T’ or ‘MT’ switch which allows them to pick up the
electromagnetic field generated by an induction loop system. The hearing aid converts this
signal into a sound suited to its user’s specific hearing requirements.
Any person with a hearing aid positioned within or near the loop can hear the loop signal by
switching their hearing aid to the correct position, allowing them to participate more effectively
in general conversation, ordering goods or services, listening to public performances, etc.
An induction loop system therefore comprises the following main elements:-
   The audio source - typically a microphone, television or radio (or a combination of these).
   The induction loop amplifier
   The loop - typically a single turn of wire usually run around the perimeter of the room or
   a special counter loop fixed to the underside of a table.
   The receiver(s) - any hearing aid with a ‘T’ or ‘MT’ switch or a specially designed loop
   listening device.

In addition to the many routine benefits for hearing aid users, induction loop systems can
also be used for other limited area broadcasting applications such as museum ‘walk
through’ guided tours and surveillance talkback systems.
The main elements of an audio-frequency induction loop system

                                      THE LOOP
        AUDIO SOURCE
                                                                  HEARING AID




                                        INDUCTION
                                           LOOP
             AUDIO SOURCE               AMPLIFIER


Some induction loop systems may require additional audio sources such as multiple
microphone or line level inputs. To facilitate this, many PDA range amplifiers include an
‘Outreach’ socket which allows the connection of multiple inputs via a range of specially
designed single gang audio connector plates. This system is described in detail on page 19.

                    A GUIDE TO AUDIO-FREQUENCY INDUCTION LOOP SYSTEMS • PAGE 4
How does an induction loop system work?
Audio-frequency induction loop systems do not use radio frequencies; they operate at audio
frequencies.

The signal from an audio source is fed into an induction loop amplifier, which amplifies and
sets the signal level in the same way as a conventional amplifier. The amplified signal,
instead of going to a loudspeaker, is fed to a closed loop of cable that is normally placed
around the perimeter of the room. Employing a constant current amplifier ensures the
current is maintained at the set level whilst providing a flat frequency response without the
need for equalization circuitry.

The current flowing through the loop generates a magnetic field that radiates in the space
around the loop cable (see diagram below). Any lines of magnetic flux that pass through the
telecoil in a receiver, such as a hearing aid, will generate a current in the coil that is then
converted back to audio and fed into the listener’s ear.

It is important to remember that the magnetic field will ‘bleed’ outside the perimeter of the
loop and therefore a loop system cannot be considered confidential. Ways of reducing this
‘bleed’ or ‘overspill’ are addressed on pages 24 and 25 of this guide.

Magnetic field in a plane through one axis of a square loop




                   A GUIDE TO AUDIO-FREQUENCY INDUCTION LOOP SYSTEMS • PAGE 5
Why we have induction loop systems
In normal use, hearing aids utilise a microphone for
                                                                         microphone
amplifying localised speech. Whilst this is effective for                                       tone
                                                               volume                           hook
local conversations/quiet environments, it is less             control
effective for listening to speech or music at a distance
or in front of a security screen at a ticket counter. This
is because the hearing aid’s microphone also picks up
any background noise in the room and unwanted
speech from other conversations. An induction loop                                     battery
system works by moving the required sound closer to                                    compartment
the hearing aid via the hearing aid’s telecoil which is         off/telecoil/mic. switch
activated by turning it to the ‘T’ or ‘MT’ position.

As telecoils are fitted as standard to most hearing aids (over 90% are said to have the ‘T’
position) induction loop systems can be considered cost-effective compared to other
hearing assistance systems. Infrared systems, for example, require special receivers, the
cost and maintenance of which must be met by the service provider.

Many modern hearing aids do not just amplify all frequencies equally; they are tailored to
suit the user’s hearing problem and amplify different bands by different amounts. This gives
maximum intelligibility, so the user has the best chance of understanding what is said.




In summary...
Induction loop systems are popular because:-
   Unwanted sounds such as other conversations and background noise are not picked up.
   No special receivers are required - telecoils are fitted as standard in most hearing aids or are
   an inexpensive option.
   Magnetic induction tends to be more reliable and effective than other systems (infrared, for
   example, is line of sight only).
   Modern hearing aids amplify different bands by different amounts to suit a user’s specific
   hearing requirements.

                    A GUIDE TO AUDIO-FREQUENCY INDUCTION LOOP SYSTEMS • PAGE 6
Where are ‘aids to communication’ required?
According to the the Royal National Institute for the Deaf (RNID):-
•   Over 9 million people are deaf or hard of hearing (one in seven of the UK population)
•   2 million of these people have hearing aids
•   1.4 million people use hearing aids regularly
•   3 million people experience significant hearing difficulties
Lobbying by organisations such as the RNID has led to increased awareness of the
difficulties faced by the hearing impaired, so much so that numerous Standards, Acts and
Schemes now recommend the provision of auxiliary aids such as induction loop systems for
the hard of hearing, as summarised below. These summaries refer to the published versions
of the documents at the time of going to press. If in doubt, full copies of these documents can
be purchased or viewed in their entirety from the organisations and/or websites indicated.

BS 8300 (2002)
                    British Standard BS 8300 is the code of practice for the design of
                    buildings and their approaches to meet the needs of disabled people.
                    The standard recommends that “a hearing enhancement system, using
                    induction loop, infra-red or radio transmission, should be installed in
                    rooms and spaces used for meetings, lectures, classes, performances,
                    spectator sports or films, and used at service and reception counters
                    where the background noise level is high or where glazed screens are
                    used” (9.3.2). It pinpoints the following areas for consideration: seated
waiting areas; ticket sales and information points; fitness suites and exercise studios;
churches; crematoria and cemetery chapels, educational, cultural and scientific buildings.
Copies of BS 8300 can be viewed at your local reference library or purchased from the British Standards
Institute, 389 Chiswick High Road, London, W4 4AL. Tel: +44 (0)20 8996 9000. Web: www.bsi-global.com


The Disability Discrimination Act (1995)
                   The aim of the DDA is to stop discrimination against disabled people
                   including the hearing impaired. Under the Act, all UK service providers,
                   i.e.,organisations offering goods, facilities or services to the general public,
                   must make ‘reasonable’ adjustments to ensure they do not unlawfully
                   discriminate against disabled people. Employers must also take measures
                   to ensure that employees are not disadvantaged in the workplace.
                   Examples of ‘reasonable adjustments’ include the provision of auxiliary
                   aids, such as induction loop systems, to enable a hard of hearing person
to access goods, facilities or services where it is impossible or unreasonably difficult for
them to do so. The DDA was strengthened in 2004 when the Disability Rights Commission’s
(DRC) Code of Practice came into effect. The DRC is an independent body, established by
Act of Parliament, which supports disabled people in getting their rights under the DDA and
gives advice to disabled people, employers and service providers.
• For more information on the DDA, visit the DRC’s website at www.drc-gb.org

                      A GUIDE TO AUDIO-FREQUENCY INDUCTION LOOP SYSTEMS • PAGE7
Building Regulations Part M1 : Access to and use of buildings (2000)
                     Current building regulations for England and Wales state that newly
                     erected or substantially reconstructed non-domestic buildings should
                     make reasonable provision for people to gain access to and use their
                     facilities (Requirement M1). In particular, the regulations state that
                     reasonable ‘aids to communication’ should be provided for the hearing
                     impaired in auditoria, meeting rooms, reception areas, ticket offices and
                     at information points. One of the aims of Requirement M1 is to ensure all
                     people can participate in proceedings at lecture/conference facilities and
                     entertainment, leisure and social venues. According to the regulations,
aids to communication will satisfy {part of} this requirement if ‘a hearing enhancement
system is installed in rooms and spaces designed for meetings, lectures, classes,
performances ... and at service or reception counters when they are situated in noisy areas
or behind glazed screens’ (section 4.36/4.36b) The regulations acknowledge that a person
with a hearing disability needs to receive a signal that is amplified in both volume and
signal-to-noise ratio and that induction loop, infrared, radio and sound field systems can
provide this advanced level of sound (section 4.35, Design Considerations).
• Building Regulations, Part M1 can be viewed at the website of the Office of the Deputy PM at www.odpm.gov.uk


Care Standards Act (2002)
                     The Care Standards Act demands that care homes in England provide
                     certain adaptations and equipment for residents, including:- ‘facilities,
                     including communication aids (e.g. a loop system), and signs to assist
                     the needs of all service users, taking account of the needs, for example,
                     of those with hearing impairment, visual impairment, dual sensory
                     impairments, learning disabilities or dementia or other cognitive
                     impairment, where necessary.’ (standard 22.6). These requirements apply
                     to all care homes providing accommodation and nursing or personal care
                     for older people in England. Regular inspections and enforcement of the
legislation is carried out by the Commission for Social Care Inspection (CSCI)
• For more information on the Care Standards Act, visit the CSCI’s website at www.csci.org.uk


The English Tourism Council’s National Accessible Scheme (2002)
                   This Scheme aims to increase accessibility for guests who are mobility,
                   hearing and visually impaired. Participation in the scheme is not
                   compulsory, but those who do are given recommendations which include
                   the provision of auxiliary aids in serviced and self-catering accommodation
                   to help satisfy the requirements of the DDA. ‘Best practice’ recommendations
                   include the fitting of a counter or portable loop system to assist hearing
                   impaired guests on booking/arrival and the installation of room loops in
                   bedrooms. Other best practice recommendations are that consideration
                   be given to providing a TV listening aid and room loop in television
lounges and that induction loops be ‘part of the standard equipment’ in conference,
entertainment and banqueting areas.
• For more information, visit www.tourismtrade.org.uk

                       A GUIDE TO AUDIO-FREQUENCY INDUCTION LOOP SYSTEMS • PAGE8
Which induction loop system should I use?
The PDA range of induction loop equipment is one of the most comprehensive in the UK.
It comprises a huge range of amplifiers, microphones, connector plates and test equipment
covering virtually every conceivable AFILS application.
Before deciding which induction loop system to use, you first need to ascertain the size of
the area to be covered in square metres (m2). Bear in mind it may not be necessary to
cover the whole of the area, for example in a church only the pews may require coverage.
To calculate the size of the area in square metres, multiply the length by the width. For
example, a room 6m x 6m in size would equal 36m2. The coverage provided by an AFILS
amplifier is also quoted in square metres. The chart below, and information in the rest of this
section, will help you select the best PDA Range product(s) for the job.

Induction loop amplifier selection chart

      PDA PRODUCT                                       SIZE OF AREA REQUIRING COVERAGE

   PL1 portable loop kit      Counters, desks,
  ML1/K counter loop kit       tables & other
 PDA102C counter loop kit      small areas up
  VL1/B1 vehicle loop kit         to 1.2m2


PDA102L/R/S small room kits          Rooms up to 49m2
 DL50/K domestic loop kit               (7 x 7m)


    AK RANGE loop kits                       Rooms up to 120m2
    PDA200E amplifier                           (11 x 11m)


   PDA200/2 professional                         Rooms up to 200m2
       loop amplifier                               (14 x 14m)

  PDA500/2 professional                                 Rooms up to 500m2
      loop amplifier                                       (22 x 22m)


  PDA1000/2 professional                                         Rooms up to 900m2
      loop amplifier                                                (30 x 30m)


Designed to meet or exceed the requirements of BS7594 and EN60118-4 when correctly
installed, all of the amplifiers in the PDA range offer excellent intelligibility, true current mode
amplification, phantom power (for electret microphones) and full compatibility with the
‘outreach plate’ audio input extension system (except the PL1, VL1 and DL50). Many are also
available in kit format for ease of specification, purchase and installation.
The entire PDA range is explained in detail over the coming pages.

                           A GUIDE TO AUDIO-FREQUENCY INDUCTION LOOP SYSTEMS • PAGE 9
1.2m2 PL1 portable induction loop system

  Ideal for restricted person to person contact
  in areas such as banks, post offices, small
  meeting rooms, reception desks, open plan
  offices and ticket booths
  Portable, lightweight design means the system
  can be moved easily from location to location
  Simple one button operation
  Integral high performance microphone
  Five years’ expected battery life under normal
  operating/charging conditions
  Auto shut-off facility (user selectable for 10,
  30 or 60 minutes) helps preserve battery life
  Unit can be used as normal whilst charging




  Typical PL1/K1 meeting room application                  Typical PL1/K1 counter/ticket booth application




at a glance...
TYPE           Portable
COVERAGE       1.2m2 approx.
DIMENSIONS     W 250 x D 300 x H 100mm (main unit); 1.7Kg
INPUTS         2 x Mic (one built-in mic. and one 3.5mm remote mic. socket for AMT or AMD mics)
INDICATORS     Power on; input level; charging required; charging in progress, audio warning of imminent shutdown.
CONTROLS       On/off button; adjust auto-shut off timer
KIT VARIANTS   PL1/K1 : PL1 amplifier, plugtop charger, ‘AFILS available’ sticker, cardboard carry case.
               PL1/K2 : PL1 amplifier, plugtop charger, FoSmeter H magnetic field strength meter/loop listening
               device; headphones, ‘AFILS available’ sticker, cardboard carry case
               PL1/K3 : As PL1/K1 but in a robust plastic storage/carry case
               PL1/K4 : As PLK/K2 but in a robust plastic storage/carry case

                    A GUIDE TO AUDIO-FREQUENCY INDUCTION LOOP SYSTEMS • PAGE 10
1.2m2 ML1/K double gang fixed counter induction loop system

  Ideal for banks, post offices, small meeting
  rooms, reception desks, ticket booths and
  any other application requiring restricted or
  small area coverage
  Requires no specialist audio experience or
  connectors - can be fitted by any competent
  electrician
  Space-saving double-gang wall-mounting
  amplifier fits standard UK 25mm back boxes
  (requires fixed mains wiring).
  Omni-directional AMT microphone (supplied)
  plugs directly into 3.5mm socket on the amplifier’s front
  Line/outreach socket also provided (max 3
  outreach plates per system)
  User-adjustable mic. sensitivity and engineer-
  adjustable loop drive and input level controls




                                                                         230V a.c




                                                                        Typical ML1/K
                                                                        counter/ticket booth
                                                                        application




at a glance...
TYPE        Wall mounting (requires fixed mains wiring and a 25mm back box)
COVERAGE    1.2m2 approx.
DIMENSIONS W 143 x H 83 x D 32mm; 300g (amplifier only)
INPUTS      1 x 3.5mm remote mic. socket; 1 x Line/Outreach socket
INDICATORS Input level; power on; loop drive meter.
CONTROLS    Mic. input level, line input level; loop drive
KIT CONTENT ML1 amplifier; AMT microphone; TX2 pre-formed counter loop; ‘AFILS fitted’ sticker.

                     A GUIDE TO AUDIO-FREQUENCY INDUCTION LOOP SYSTEMS • PAGE 11
1.2m2 PDA102C free-standing counter induction loop system

  Ideal for banks, post offices, small meeting
  rooms, reception desks, ticket booths and
  any other application requiring restricted
  or small area coverage
   Includes a 3.5mm microphone input (for
   use with the AMT microphone supplied)
   and a line/outreach socket
   Adjustable drive control allows the
   amplifier’s output stage to be set-up to suit
   the exact characteristics of any room
   State-of-the-art audio processor features
   an automatic gain control which
   compensates for poor microphone
techniques and helps suppress loud noises,
hisses and clicks
   Designed to be free-standing or wall-mounted
   using the keyholes provided




                                                                       Typical PDA102C
                                                                       counter/ticket booth
                                                                       application




 at a glance...
TYPE        Free-standing/wall mountable. Plugtop mains lead supplied.
COVERAGE    1.2m2 approx.
DIMENSIONS W 136 x H 56 x D 178mm (amplifier only); 1.25Kg
INPUTS      1 x 3.5mm remote mic. socket; 1 x Line/Outreach socket
INDICATORS Input level; loop current; power on
CONTROLS    Combined input level; loop drive
KIT CONTENT PDA102 amplifier; AMT microphone; TX121 pre-formed counter loop; ‘AFILS fitted’ sticker

                     A GUIDE TO AUDIO-FREQUENCY INDUCTION LOOP SYSTEMS • PAGE 12
1.2m2 VL1/B1 12V vehicle induction loop system

  Ideal for cars, taxis, buses and other private/commercial vehicles

  Kit includes a compact mini-induction
  loop amplifier (pictured right) with
  keyholes for dashboard mounting, a
  cigarette lighter power adaptor, an
  AMT microphone, a pre-formed loop
  and an ‘AFILS fittted’ sticker
  Amplifier operates at 12V d.c. (24V vehicle kit also available, order code VL1/B2)
  Loop can be positioned in the vehicle’s roof lining, under a seat, across the back of a
  seat or in a door panel to suit the application
  Metal compensation control helps combat the frequency response problems caused by
  metal ‘absorbing’ the magnetic field
  Optional VL9 lead available for connection to the vehicle’s audio system




at a glance...
TYPE           Dash mounting; 12V
COVERAGE       1.2m2 approx.
DIMENSIONS     W 120 x H 31 x D 60mm; 220g.
INPUTS         1 x 3.5mm remote mic. socket; 1 x line
INDICATORS     Input level, loop current, power on
CONTROLS       Mic level; Line level, loop drive, metal compensation
KIT VARIANTS   VL1/B1: VL1 Amplifier; TX2 Pre-formed loop; AMT microphone; AL8 Fused cigarette lighter power
               adaptor; ‘AFILS fitted’ sticker
               VL1/B2 : VL1 Amplifier; TX2 Pre-formed loop; AMT microphone; VL1PSU24 24V to 12V convertor;
               AL7 2.5mm DC power plug to bare end lead; ‘AFILS fitted’ sticker.


                    A GUIDE TO AUDIO-FREQUENCY INDUCTION LOOP SYSTEMS • PAGE 13
50m2 PDA102L/R/S small room induction loop systems

  Three variants available
  PDA102L ideal for use in small meeting rooms,
  council chambers, doctor surgeries, etc.
  PDA102R ideal for small room applications where
  equipment needs be mounted above suspended
  ceilings, etc.
  PDA102S ideal for use in nursing home TV lounges
  Includes a 3.5mm microphone input
  and line/outreach socket
  Designed to be free-standing or
  wall-mounted using the keyholes
  provided




                                                       Typical PDA102S TV lounge application




 Typical PDA102L meeting room application                 Typical PDA102R meeting room application
                                                          Note that the APM plated microphone supplied in the
                                                          PDA102R kit provides direct speech coverage of 2.5m


at a glance...
                                                          so in larger rooms you may need to fit more.



TYPE           Free-standing/wall mountable. Plugtop mains lead supplied.
COVERAGE       50m2 approx.
DIMENSIONS     W 136 x H 56 x D 178mm (amplifier only); 1.25Kg
INPUTS         1 x 3.5mm remote mic. socket; 1 x Line/Outreach socket
INDICATORS     Input level; loop current; power on
CONTROLS       Combined input level; loop drive
KIT VARIANTS   PDA102L: PDA102 amplifier; AMT tie/desk microphone; 30m loop cable; ‘AFILS fitted’ sticker
               PDA102R: PDA102 amplifier; APM plated microphone; 30m loop cable; ‘AFILS fitted’ sticker.
               PDA102S: PDA102 amplifier; APL dual phono outreach plate, APS Scart lead; 30m loop cable;
               ‘AFILS fitted’ sticker


                    A GUIDE TO AUDIO-FREQUENCY INDUCTION LOOP SYSTEMS • PAGE 14
50m2 DL50/K domestic induction loop system

  Free-standing - ideal for bedrooms, living rooms,
  TV lounges, studies and other domestic applications
  Simple to adjust, tamper-resistant drive, level, tone
  and mic. priority controls
  Input peak, output current, signal present and power
  on LEDs
  Alert tone input for doorbells, fire alarms, security
  systems, etc.




    Typical DL50/K domestic TV lounge application




at a glance...
TYPE        Free standing, Plugtop mains lead supplied.
COVERAGE    50m2 approx.
DIMENSIONS W 185 x H 40 x D 85mm (amplifier only); 550g
INPUTS      2 x 3.5mm microphone sockets, 1 x dual phono (line) socket, 1 x alert
INDICATORS Input level; loop current meter; power on
CONTROLS    Input level, loop drive, tone, microphone priority
KIT CONTENT DL50 amplifier, plug-top power supply, 33m of loop cable, SCART-to-double-phono lead, AMT
            microphone, ‘AFILS fitted’ sticker


                    A GUIDE TO AUDIO-FREQUENCY INDUCTION LOOP SYSTEMS • PAGE 15
120m2 AK Range induction loop amplifiers and kits

  Available in a wide range of kit formats -
  suitable for use in meeting rooms, waiting
  rooms, TV lounges, health and fitness suites,
  churches, etc (see kit list below)
  PDA200E amplifier includes straightforward
  internal screw connectors
  Wall-mounting metal enclosure for
  permanent installation
  Internal drive, level and tone controls




                                                                                         Note that the APM plated
                                                                                         microphone supplied in the
                                                                                         AKM1 kit provides direct
                                                                                         speech coverage of 2.5m so in
                                                                                         larger rooms you may need to
                                                                                         fit more.


                Typical AKM1 meeting
                room application

at a glance...
TYPE           Wall mounting, requires fixed mains wiring
COVERAGE       120m2 approx.
DIMENSIONS     W 271 x H 200 x D 77mm (amplifier only); 2.82kg
INPUTS         1 x Microphone, 1 x Line/Outreach, 1 x Alert and 1 x 100V line (all screw type connectors)
INDICATORS     Input level; loop drive meter; power on
CONTROLS       Input level, loop drive, tone
KIT VARIANTS   AKM1 Meeting room kit: PDA200E amplifier; APM plated mic.; ‘AFILS fitted’ sticker
               AKR1 Waiting room kit: PDA200E amplifier; APL outreach plate (paging system input); ‘AFILS fitted’ sticker
               AKT1 TV / music lounge kit: PDA200E amplifier; AMH handheld mic.; APS scart lead; APJ outreach
               plate; APL outreach plate; ‘AFILS fitted’ sticker.
               AKL1 Lecture room kit: PDA200E amplifier; AMT tie/desk mic.; AML lectern mic.; 2 x APJ outreach
               plates; ‘AFILS fitted’ sticker.
               AKU1 Retail unit kit: PDA200E amplifier; AML lectern mic.; APJ outreach plate; ‘AFILS fitted’ sticker.
               AKW1 Place of worship kit 1: PDA200E amplifier; AML lectern mic.; APJ outreach plate; APL
               outreach plate (audio input for CD/tape deck); ‘AFILS fitted’ sticker.
               AKW2/L Place of worship kit 2 (lavalier version): PDA200E amplifier; AMR/LA lavalier radio
               mic; APQM outreach plate, 2 x APXM outreach plates (for existing mics.); ‘AFILS fitted’ sticker.
               AKW2/H Place of worship kit 2: as AKW2/L but with a handheld radio mic.instead of a lavalier mic.
               AKH1/L Health & fitness club kit (lavalier mic. version): PDA200E amplifier; AMR/LA lavalier radio
               mic; APQM outreach plate, APL outreach plate (for CD/tape deck); ‘AFILS fitted’ sticker.
               AKH1/H Health & fitness club kit: as AKW1/L but with a handheld radio mic.instead of a lavalier mic.

                    A GUIDE TO AUDIO-FREQUENCY INDUCTION LOOP SYSTEMS • PAGE 16
200m2 to 900m2 PDA Pro-range induction loop amplifiers

 Ideal for theatres, cinemas, churches,
 conference halls and other applications
 where top quality sound is a must
 Each unit includes two XLR 3-pin input
 sockets (one balanced mic. and one
 switchable balanced mic./line) and one
 outreach connector.
 Adjustable level controls provided for all
 inputs - can be used individually or
 together as a three-input mixer
 Metal compensation control helps offset the frequency
 response problems associated with excessive metal in a
 building
 Includes a true output current meter
 and provides visual indication of
 the amplifier’s compressor action
 via two LEDs
 3.5mm headphone socket
 allows true monitoring of the
 output signal
 Advanced audio signal processing
 with automatic gain control




                                                                               Typical PDA Pro-Range
                                                                               place of worship application




at a glance...
TYPE         Free-standing (optional wall or 2U 19” rack mount kits available); plugtop IEC mains lead provided
COVERAGE     200m2 (PDA200/2); 500m2 (PDA500/2); 900m2 (PDA1000/2)
DIMENSIONS   W 380 x H 80 (2U) x D 220mm; 3.74kg (PDA200/2), 3.46kg (PDA500/2); 4.54Kg (PDA1000/2)
INPUTS       2 x XLR (one mic.; one mic/line) and one outreach connector
INDICATORS   Loop drive meter; compression (high/low); power on
CONTROLS     3 x input level controls, loop drive, metal compensation, on/off switch

                  A GUIDE TO AUDIO-FREQUENCY INDUCTION LOOP SYSTEMS • PAGE 17
Microphones
Electret microphones have the highest tolerance of magnetic feedback and are therefore
recommended for induction loop systems. Dynamic microphones should not be used as
they contain moving coil magnets which can be affected by the magnetic field generated by
the loop.

Phantom power is provided on all PDA range amplifiers, so electret microphones with
internal batteries are not necessary.

When deciding which electret microphone to use, the following guide should prove useful.


APPLICATION / MICROPHONE TYPE                                  MODEL NO.

Conference table (centre of tabletop, counter, etc)            AMT tie/desk mic
                                                               APM plated mic
                                                               AMH handheld mic + stand
                                                               AMP* professional handheld mic + stand

Lectern (for pulpits, lectures, etc)                           AML fixed gooseneck mic, long stem
                                                               AMLS fixed gooseneck mic, short stem
                                                               AMD movable gooseneck mic, long stem
                                                               AMDS movable gooseneck mic, short stem

Lavalier (for the lapel of an after dinner speaker)            AMT tie/desk mic
                                                               AMR/LA, B or C (radio mic)

Ambient mic (for audience response etc)                        APM at distances of ≤2.5m
                                                               PRO45 at distances ≥ 2.5m

Ceiling (recessed in the ceiling above a table)                APM at distances of ≤2.5m
                                                               PRO45 at distances ≥ 2.5m

Desk Microphone with Push To Talk (PTT)                        AMD/P (as AMD with PTT)

Handheld                                                       AMH handheld mic
                                                               AMP* professional handheld mic
                                                               AMR/HA, B or C (radio mic)

* All PDA range microphones are supplied with a connection lead apart from the AMP. If
using an AMP, a range of connection leads are available, contact our sales desk for details.
To avoid interference, microphone cables should be sited at least one metre away from loop
cable.
                      A GUIDE TO AUDIO-FREQUENCY INDUCTION LOOP SYSTEMS • PAGE 18
The Outreach Plate audio input extension system
The Outreach Plate audio input extension system comprises a range of wall, ceiling and
desk mountable single gang audio input plates specifically designed to increase the audio
input capability of an induction loop system.
Covering the most common variants of audio connector, they work by mixing the signals
from various audio input sources into one balanced line level input which can be fed into the
line input of a compatible amplifier.
Mountable on 25mm single gang back boxes, each plate features a built-in mixer, pre-amp,
input level control and balanced output. The fact they can be installed at the most
convenient point on an installation overcomes the need for excessively long and potentially
hazardous microphone/audio leads.
Typically, up to 10* Outreach plates (any mix) can be daisy-chained to one balanced line
level input with cable lengths of up to 100m easily achievable using standard two-pair audio
cable with no recognisable degradation of audio signal quality.
Each outreach plate requires four wires, two balanced line (A +, A –), one ground (0V) and
one power connection (12-32 V DC regulated). To facilitate their straightforward
connection, most PDA Range amplifiers are fitted with an Outreach connection socket
as standard.

Example wiring to equipment fitted with an ‘Outreach’ socket
                                OUTREACH              OUTREACH          AMPLIFIER
                                  PLATE                 PLATE           OUTREACH
                                OUTREACH              OUTREACH          AMPLIFIER
                                                                       CONNECTOR
                                  PLATE                 PLATE           OUTREACH
     to optional next       A IN +    A OUT +    A IN+       A OUT +   CONNECTOR+
                                                                                A
        outreach next
     to optionalplate       A IN –
                            A IN +    A OUT –
                                      A OUT +    A IN+–
                                                 A IN        A OUT –
                                                             A OUT +            A–
                                                                                A+
     (max. 10* plates
       outreach plate        V+
                            A IN –    A OUT –     V+
                                                 A IN –      A OUT –            V+
                                                                                A–
            per system)      GRND
     (max. 10* page 1
     * see note onplates    V+
                                                  GRND
                                                 V+                             Gnd
                                                                                V+
            per system)     GRND
     * see note on page 1                         GRND                          Gnd


If you wish to connect Outreach plates to an audio system that has a line level input but not
a 12-32V auxiliary output, an external 24V 250mA d.c. regulated power supply (part no.
APV) can be used, as detailed below:

Example wiring to equipment that does not have a 12-32V d.c. output

                                OUTREACH              OUTREACH
                                  PLATE                 PLATE
                                OUTREACH              OUTREACH
                                  PLATE                 PLATE
      to optional next      A IN +               A IN+
                                                                            To
                                      A OUT +                A OUT +
                                                                            balanced
     to optionalplate
        outreach next       A IN –    A OUT –    A IN –      A OUT –        To
                            A IN +    A OUT +    A IN+       A OUT +        line level
      (max. 10* plates       V+                   V+                        balanced
       outreach plate       A IN –    A OUT –    A IN –      A OUT –        input of
            per system)      GRND                 GRND                      line level
     (max. 10* plates       V+                   V+                         amplifier
     * see note on page 1                                                   input of
            per system)     GRND                 GRND                       amplifier
     * see note on page 1                                                     APV
                                                                          24V 250mA
                                                                             APV
                                                                              PSU
                                                                          24V 250mA
* Only 3 Outreach plates can be connected to ML1 amplifiers.                  PSU


                      A GUIDE TO AUDIO-FREQUENCY INDUCTION LOOP SYSTEMS • PAGE 19
Outreach plate variants

                  APM OMNI-DIRECTIONAL PLATED MICROPHONE
                  A self-contained omni-directional electret microphone complete with
                  onboard mic to line level converter. Typical coverage up to 25m2 (ambient)
                  or 2.5m (direct speech) when located at a ceiling height of 2.5-3m.


                  APL DUAL PHONO LINE LEVEL PLATE
                  Accepts stereo phono line-level signals (usually from a stereo source
                  such as a TV). Includes an on-board stereo phono to mono converter.
                  (An APS SCART to dual phono lead is also available).


                  APJ 3.5mm MICROPHONE JACK PLATE
                  Accepts unbalanced electret microphones with 3.5mm mono jack plugs.
                  Includes an onboard mic to line level converter, high gain pre-amplifier
                  and 8V phantom power.


                  APQM 6.35mm (1/4”) MICROPHONE JACK PLATE
                  Accepts balanced or unbalanced electret microphones with 6.35mm
                  (1/4”) jack plugs. Includes an on-board mic to line level converter, high
                  gain pre-amplifier and 8V phantom power.

                  APXM XLR 3 PIN MICROPHONE PLATE
                  Accepts balanced or unbalanced microphones with standard 3 pin XLR
                  connectors. Includes an on-board mic to line level converter, high gain
                  pre-amplifier and 8V phantom power.


                  APXL XLR 3 PIN LINE LEVEL PLATE
                  Accepts standard 3 pin XLR feeds from audio equipment such as stage
                  or church mixing desks, etc.



                  APQL 6.35mm (1/4”) LINE LEVEL PLATE
                  Accepts 6.35mm (1/4”) jack feeds from audio equipment such as stage
                  or church mixing desks, etc.



                  API ‘AFILS ACTIVE’ PLATE
                  Includes two ultra-bright LEDs in a translucent diffuser overprinted with
                  the AFILS ‘ear’ symbol. The LEDs illuminate when the Outreach network
                  is powered to indicate that an AFILS system is installed.


Also available: The APSS phase shifter, see page 24 for details.


                  A GUIDE TO AUDIO-FREQUENCY INDUCTION LOOP SYSTEMS • PAGE 20
Induction loop cable
There is nothing electrically special about induction loop cable. Almost any stranded or
solid single core cable with tough insulation can be used, provided it is not liable to break
(to minimise the chance of it shorting to earth and damaging the amplifier’s output) and is of
the appropriate gauge and DC resistance (0.5 to 1 Ohm).

If purchasing a PDA range induction loop kit, always use the loop cable supplied with the
kit. If purchasing an amplifier that does not include loop cable, refer to the loop cable
selection chart below.
                300
                                                                                                          1 Ohm
                250
                200
 Cable Length




                175
                150
                125                                                                                      0.5 Ohm
                100
                75
                50
                25
                0
                      0      0.5       1       1.5         2   2.5     3     3.5   4       4.5      5

                                                           Cable CSA (mm2)

The chart shows the recommended CSA (cross-sectional area) for different lengths of loop
cable. Simply work out the length of the loop required and choose a cable size that falls into
the non-shaded area of the graph. For example, to cover a room 30m x 20m (600m2) the
loop cable would need to be 100m long (2 sides @ 30m and 2 sides @ 20m). The
recommended cable CSA for a loop this length is between 2mm2 and 4mm2. Therefore, a
PDA1000/2 (which can cover areas up to 900m2) using 2.5mm2 cable would be sufficient.

The following loop cable is available from your PDA range distributor, all in 100m reels:-
       0.5mm2             white    single   core   cable   (LOOP1/W)         0.5mm2    black   single   core   cable   (LOOP1/B)
       1.0mm2             white    single   core   cable   (LOOP2/W)         1.0mm2    black   single   core   cable   (LOOP2/B)
       1.5mm2             white    single   core   cable   (LOOP3/W)         1.5mm2    black   single   core   cable   (LOOP3/B)
       2.5mm2             white    single   core   cable   (LOOP4/W)         2.5mm2    black   single   core   cable   (LOOP4/B)

Note that flat copper foil tape is also available and some installers prefer to use this as a floor
loop under light duty carpets. Three sizes are available with cross sections of 0.5 mm2 (part
no. FLAT1005), 1.0mm2 (part no. FLAT2005) and 1.5mm2 (part no. FLAT3005). Protective
tape will also be required to hold the cable down and reduce the likelihood of damage. Copper
foil tape should be connected to the loop amplifier using solder or 1A ‘choc’ block.

Note that the chemical elements of some self-levelling floor compounds can react with the
plastic covering of copper foil tape. If installing the loop under self levelling compound, we
recommend you check their compatibility by covering a small piece of the tape with the
compound to be used and look for any adverse reaction.

                                      A GUIDE TO AUDIO-FREQUENCY INDUCTION LOOP SYSTEMS • PAGE 21
Induction loop system design and installation
Induction loop system design and installation can be simple provided that a few basic facts
are understood.
Maximum area coverage
The approximate coverage provided by an AFILS amplifier is usually quoted in metres
squared (m2). For example, the 120m2 quoted for our PDA200E amplifier means that the
PDA200E can cover rooms up to 11 x 11m in size. The PDA range has amplifiers that can
cover everything from a 1.2m2 ticket counter to a large 900m2 conference hall.
Note that in certain installations, it may not be necessary to cover the whole room, i.e., in a
bowling alley the loop may only need to cover the top of the lanes.
Loop amplifier position
Induction loop amplifiers are best sited adjacent to the loop, as the feed cable will generate
a magnetic field that may interfere with other areas. However, if a long feed cable cannot be
avoided, the cable should be twisted to reduce magnetic radiation.
Loop cable position
Under current IEEE wiring regulations (17th Edition), loop cable is a classified as class 2A
and, as such, must be sited at least 600mm away from telephone, mains and control cables.
In most installations, loop cable is usually run around the perimeter (edge) of the room.
The field strength in the plane of the loop (the height
at which the cable is positioned) varies greatly so it is           Try to locate loop cable approx. 1.2m
                                                                    above or below loop listening height.
best to install the loop above or below the listener at
floor or ceiling height. The loop field will not be as
strong but it will be much more even and provide
better results. Do not mount the loop cable behind 3m
                                                                                        Typical listening height


dado rails as the loop signal will be uncomfortably
strong for the hearing aid user.
Try to locate ceiling loops approximately 1.2m above
                                                             1.8m



the listener’s head (listening height with the hearing
                                                            1.2m


aid user sitting or standing is normally 1.2 to 1.8m
from the floor). Note that when using a ceiling
mounted loop, approximately 20% of the amplifier’s
power will be lost for every 1.5m increase in height so the cable should never be mounted
higher than 7m above listening height.
Structural steel, in particular, large sheets of metal (solid or perforated) such as metal
suspended ceilings, can absorb the magnetic field resulting in uneven coverage or dead
spots. To avoid the magnetic field being absorbed by structural steel, if possible keep the
loop about a metre from large uprights.
If there is a steel-reinforcing grid in the floor, either put the loop in the ceiling or, if it must go
in the floor, install the loop in plastic conduit as far above the grid as possible. The
amplifier’s drive current may have to be turned up to overcome the effects of the metal, so
choose the largest conductor size possible to suit the area.

                    A GUIDE TO AUDIO-FREQUENCY INDUCTION LOOP SYSTEMS • PAGE 22
If an application has a suspended ceiling with a metal grid and non-metallic ceiling tiles, tie-
wrap the loop cable to the support wires a couple of centimetres above the tiles. If the tiles
are metallic, the field strength will be affected, especially if they are electrically cross-
bonded although it may be possible to partially overcome this by increasing the drive control
on the amplifier. If single core cable fails to provide the required field strength in such
applications, consider using three core cable and choc block to create three loops in series.
Although this technique increases field strength it also reduces the top-end audio frequencies
making the loop sound bass heavy, however this can be redressed using the metal
compensation control on the PDA Pro-Range of amplifiers or the tone control on a PDA200E.
On floor loops, avoid running the loop up and over door openings as there will be a ‘dead
spot’ (i.e. no signal) when the hearing aid user passes through. At doors and windows, the
loop cable can pass vertically up and down either side. However, this wastes some power
so care should be taken if the amplifier is only just capable of covering the area. Generally,
we would suggest allowing 20% extra power in the amplifier if vertical runs are needed.
In applications with flat ceilings and sloping floors (cinemas, theatres, etc), try to run the
loop at the same angle as the floor, perhaps behind a non-metallic handrail (if one is
available) to ensure the signal is distributed evenly throughout the building.
Always run a trial loop and test to evaluate performance by listening to the signal with either
a hearing aid or a dedicated loop listening device. To ensure the system complies with
BS7594 we recommend you also test the system using a pink noise generator and
magnetic field strength meter.
Dead spots
In the region directly above or below the loop cable, the signal will drop to zero. This is
because a hearing aid’s coil only responds to the vertical component of magnetic field.
The higher the loop is placed, the wider the dead spot immediately over and under the
cable will be.
Overspill
The signal generated by the induction loop will
appear outside as well as inside the loop -
sometimes up to three times the loop width away.
This is often referred to as ‘overspill’. Similarly, a
loop placed at ceiling height gives excellent
coverage in the room above and a loop placed at
floor level will cover the room below. Placing the
downstairs loop in the floor and the upstairs loop in
the ceiling will reduce the problem but if the loops
are large the overspill may still be unacceptable.
The importance of overspill depends on the application. For instance, it will probably not
matter if a church service can be picked up in the church grounds. However, should the
signal from one loop system interfere with another in a multi-screen cinema, or a
confidential loop signal in a police station be picked up by an unauthorised person in a
neighbouring room, this is more concerning. BS7594 suggests several technically complex
solutions to prevent overspill that are reasonably effective but rarely employed due to high
cost. In many cases overspill can be reduced nearly as effectively and for much less cost,
using the special loop patterns described overleaf.
                   A GUIDE TO AUDIO-FREQUENCY INDUCTION LOOP SYSTEMS • PAGE 23
‘Low overspill’ reduced sized loops
One of the most obvious and cost-effective ways of reducing overspill is to install a reduced
sized loop within the area requiring coverage. We can estimate how much overspill there will
be by looking at the width of the loop (which controls the overspill). For example, if we look at
the following diagram of a 4m x 6m perimeter loop you can see the signal overspills outside
the room before dropping off to an inaudible level at around 12 metres.




Logically, if we wanted to reduce the overspill we can move the loop into the room moving
the overspill with it, thus:-




It is important to remember there will be a dead spot immediately above or below the loop
cable and that anyone sitting over it won’t hear anything (this is due to the fact that hearing
aid coils only respond to the vertical component of the magnetic field). However, unless the
loop is a long way above or below the listener, this ‘dead’ spot will be very narrow and it is
often an acceptable compromise in return for reduced overspill. In our experience, the loss
of some areas in the room to hearing aid users is accepted as a ‘reasonable provision’ as
long as the person responsible for the room is made aware of this.

‘Low overspill’ phase-shifting loops
For applications where minimal overspill and consistent coverage throughout the site (i.e.
no dead spots) is essential, you may wish to consider using an APSS phase shifter. This is
a more costly and time-consuming method than the reduced size loop described earlier but
it will avoid any deadspots being formed inside the loop. The APPS is designed to work with
the Outreach Plate audio input extension system (see page 19). It works by taking the
signal from one or more Outreach plates and producing two signals that are 90° out of

                   A GUIDE TO AUDIO-FREQUENCY INDUCTION LOOP SYSTEMS • PAGE 24
phase with each other. These signals are then fed into two (identical) induction loop
amplifiers which are in turn connected to two induction loops laid out in a special
overlapping pattern. The resultant magnetic field is evenly spread within the area being
covered but the strength falls off much more quickly than normal outside the loop.

   Audio
   Source                                                     Amp #1                   Loop # 1
                                                                                  Must be laid out in
                                                                                 the special pattern,
                                                Balanced
                                                    audio
                                                                                 detailed in the main
                 Balanced                                                         APSS instructions
                  audio
                                     +45°
           DC               DC      DC in
                                                                                       Loop # 2
            in              out       -45°             DC
                                                       out                        Must be laid out in
  Outreach                     Phase                                             the special pattern,
                                                Balanced                         detailed in the main
  Plate(s)                     Shifter
                                                    audio                         APSS instructions
 For more detailed information please request a copy          Amp #2
 of our main APPS instructions.
                        Special loop patterns:
‘Low overspill’ fixed table loops
                               fixed tables
This pattern restricts the loop to the immediate vicinity of the table and, depending on the
layout, there should be little or no overspill outside the room. The area of the loop is the overall
                 Restricts the loop to the immediate vicinity with little or no overspill
length x the width, ignoring the shape of the pattern. The perimeter is the actual cable length
and this may result in a larger cable diameter being required than for a rectangular loop.




Mains hum
Some buildings have an underlying 50Hz hum present, especially old properties where live
and neutral wiring takes separate routes, resulting in a loop. However, most hearing aids
are designed to reject such low frequencies, and so this is not normally a practical problem.
Interference
Induction loops will interfere with other equipment, i.e., electric guitars will definitely pick up
the magnetic field and cause feedback although some are less sensitive. If listeners can hear
a hum when the loop system is operating, turn the amplifier off completely and test for noise
using a hearing aid or a loop listening device. The noise should still be present and proves it
cannot be due to the loop amplifier. We recommend this be tested for before installation.

                      A GUIDE TO AUDIO-FREQUENCY INDUCTION LOOP SYSTEMS • PAGE 25
Damage to the loop
A simple break can be repaired provided it can be found. All that matters is that the join is
low resistance and allows the required current to flow through the loop. If the loop cable is
shorted to earth, for instance, by drilling through it and touching a reinforcing grid, the
amplifier output stage will be damaged. This cannot be protected against.
The isolation issue
When a hearing aid user switches his or her hearing aid to the ‘T’ position, its on-board
microphone is switched off and the only noise that can be heard is the loop signal. If the
system is connected to just one sound source, such as a TV, some hearing aid users say
the lack of background noise makes them feel isolated. This can be overcome by
positioning a microphone where it will convey background noise and pick up general
conversation - this can be easily achieved using our Outreach input extension system.
Vertical loops
Virtually all loops are laid in the horizontal (as around the
skirting board). This is due to the directional response of
the hearing aid (see diagram right). However, in an
application such as a hospital where the hearing aid
wearer is predominantly lying down then no signal will be
received. It is therefore necessary to run the loop cable at
an angle of 45 degrees from floor to ceiling as this will
allow the hearing aid to cut across the plane and receive
a signal.
In summary...
Each induction loop system can bring with it its own set of problems and issues.
Before designing a system, try to find answers to the following questions. Once you have the
answers, the information in this guide will help you provide an effective solution.
   What is the area used for (reception, meeting room, lecture theatre, etc)?
   Do you require an audio input from a TV/Video?
   Do you require an input from an existing PA system?
   Do you require fixed or mobile microphones?
   How many microphone positions are required?
   Do any rooms next or close to the area require a separate system?
   What are the dimensions of the area - length, width and height?
   Where can the loop cable be installed - ceiling / floor void, in floor screed, under floor
   covering or wall?
   What is the ceiling height and how is it constructed?
   Is there any steel or other metals around the building?
   Is there any risk of theft to the equipment?
   Does it need to be a ‘secure’ system with little overspill?




                    A GUIDE TO AUDIO-FREQUENCY INDUCTION LOOP SYSTEMS • PAGE 26
Testing an induction loop system
General testing
We recommend all induction loop systems are tested using our ‘FoSmeter H’ loop listening
device (order code AHHM/H) and a set of 32 Ohm headphones (order code HEAD1).
With all relevant audio inputs active, start by listening to the loop signal
in the centre of the loop. If the signal level is not acceptable, adjust
the drive control on the amplifier in small increments until it is. When
you are satisfied with the signal in the centre of the loop, move around
the room to ensure coverage is consistent throughout. Pay particular
attention to areas where hearing aid users are likely to gather.
The ‘FoSmeter H’ comes with a built-in magnetic strength meter.
The meter’s red peak indicator (the fifth LED on the gauge) should
only illuminate with peaks in the input signal - if it is lit too frequently,
the audio sound quality will be distorted and the amplifier may
overheat. If this is the case, try adjusting the layout of the loop and/or
consider purchasing a more powerful amplifier. If it is impossible to
illuminate all of the indicators on the magnetic strength meter even
when the DRIVE control is turned fully clockwise, the thickness (CSA)
of the induction loop cable used may be insufficient. Refer to page 21,
to ensure you are using the recommended cable for the application.

Testing to BS7594
For compliance with BS7594 (the code of practice for audio-frequency induction loop systems),
we recommend you also check the system using a pink noise generator as the system’s audio
source. BS7594 recommends what the magnetic field strength over a covered area should be
and we believe the most efficient way of ensuring this is achieved is to measure the field
strength of a steady output. Unlike music or speech (both of which provide a variable sound
output from which it is virtually impossible to obtain an accurate RMS reading), pink noise has
an equal and constant average amount of energy content per octave of bandwidth. When fed
into loop system, pink noise therefore gives a constant field strength which can be easily and
accurately measured using a magnetic field strength meter.
The following PDA range test equipment is available:-
  FoSmeter H         Combined magnetic field strength meter & loop listener (part no. AHHM/H)
  FoSmeter+          Combined pink noise generator & magnetic field strength meter (part no. AMPN)
  FoSmeter           Magnetic field strength meter only (part no. AHHM)
  PNGN               Pink noise generator only (part no. PNGN)
  AL1                3.5mm jack (for PNGN) to 3.5mm jack lead
  AL2                3.5mm jack (for PNGN) to double phone lead
  AL3                3.5mm jack (for PNGN) to bare ended lead
  HEAD1              Headphones for use with FosMeter H



                     A GUIDE TO AUDIO-FREQUENCY INDUCTION LOOP SYSTEMS • PAGE 27
Key features of the PDA Range of AFILS testing equipment

             PNGN
               Can be connected to the line level input of most AFILS amplifiers
                Has a fixed level output of 400V rms and a crest factor of 4:1
                Note that a selection of 10m long connection leads (AL1, AL2 and
                AL3 are available)
                Requires 1 x PP3 battery (not supplied)


             FOSMETER
               Accurately measures the magnetic field strength of any AFILS system
                Calibrated at manufacture for accuracy and linearity
                Includes ten LEDs laid out in 3dB increments
                Two switches - Normal/A-weight Filter and High/low Gain
                Requires 1 x PP3 battery (not supplied)




             FOSMETER H
               Combines the functions of a magnetic field strength meter and loop
               listening device in one unit
                Allows conventional audio signals such as music or speech to be
                tested for distortion using 32 Ohm headphones (part no. HEAD1)
                The unit’s gain switch is set to operate in low mode only to prevent
                interference from mains hum when listening to the system
                Requires 1 x PP3 battery (not supplied)


             FOSMETER +
               Combines the functions of a pink noise generator and magnetic field
               strength meter.
                We recommend the FoSmeter + is used for testing small installations
                only as it is not practical to have a long lead trailing from a pink noise
                output socket to the AFILS amplifier.
                Requires 1 x PP3 battery (not supplied)




             A GUIDE TO AUDIO-FREQUENCY INDUCTION LOOP SYSTEMS • PAGE 28
Full PDA range parts listing
PORTABLE INDUCTION LOOP KITS (approx. 1.2m2 coverage)

PL1/K1          Portable induction loop kit (supplied in a cardboard storage/carry case)
                Includes PL1 amplifier c/w battery & integral microphone, plugtop charger and sticker.
PL1/K2          Portable induction loop kit with AFILS tester (supplied in a cardboard storage/carry case)
                Includes PL1 amplifier c/w battery & integral microphone, plugtop charger, sticker,
                AHHM/H combined FoSmeter H magnetic field strength meter/loop listener and headphones.
PL1/K3          Portable induction loop kit (supplied in a robust plastic storage/carry case)
                Includes PL1 amplifier c/w battery & integral microphone, plugtop charger and sticker.
PL1/K4          Portable induction loop kit with AFILS tester (supplied in a robust plastic storage/carry case)
                Includes PL1 amplifier c/w battery & integral microphone, plugtop charger, sticker,
                AHHM/H combined FoSmeter H magnetic field strength meter/loop listener and headphones.
PL1/BATT        Replacement battery for PL1 amplifier

1.2m2 COUNTER INDUCTION LOOP KITS
ML1/K           ML1 counter induction loop kit
                c/w ML1 wall-mounting double gang loop amplifier, AMT mic. and TX2 counter loop
PDA102C         PDA102 counter induction loop kit
                c/w PDA102 free-standing loop amplifier, AMT microphone and TX121 counter loop

1.2m2 VEHICLE INDUCTION LOOP KITS
VL1/B1          12V vehicle induction loop kit
                c/w VL1 mini-12V induction loop amplifier, AL8 Fused cigarette lighter to 2.5mm DC power connector,
                TX2 pre-formed loop, AMT microphone
VL1/B2          24V vehicle induction loop kit
                c/w VL1 mini-12V induction loop amplifier, AL7 2.5mm DC power connector to bare ended lead,
                24V to 12V DC convertor, TX2 pre-formed loop, AMT microphone

50m2 INDUCTION LOOP AMPLIFIERS & KITS
DL50/K          DL50 50m2 Domestic induction loop amplifier kit
                c/w DL50 free-standing loop amplifier, AMT tie/desk mic., APS scart lead & loop cable
PDA102L         PDA102 50m2 Small room loop kit (tie/desk mic version)
                c/w PDA102 free-standing loop amplifier, AMT tie/desk microphone and loop cable
PDA102R         PDA102 50m2 Small room loop kit (omni-directional plated mic. version)
                c/w PDA102 free-standing loop amplifier, APM plated microphone and loop cable
PDA102S         PDA102 50m2 TV lounge loop kit
                c/w PDA102 free-standing loop amplifier, Scart lead and APL connection plate and loop cable

120m2 INDUCTION LOOP AMPLIFIERS & KITS
Please note: Loop cable is not included in the following ‘AK’ range kits. We recommend you use 1mm2 single core
cable such as our LOOP2/W cable which is available in 100m reels..
PDA200E         PDA200E 120m2 wall-mounting induction loop amplifier
AKM1            PDA200E 120m2 Meeting/seminar room loop kit
                c/w PDA200E amplifier,APM omni-directional mic plate
AKL1            PDA200E 120m2 Lecture room loop kit
                c/w PDA200E amplifier, AMT tie/desk mic, AML lectern mic, 2 x APJ plate

                       A GUIDE TO AUDIO-FREQUENCY INDUCTION LOOP SYSTEMS • PAGE 29
AKT1           PDA200E 120m2 TV / music lounge loop kit
               c/w PDA200E amplifier, AMH handheld mic, APS scart lead, APJ plate, APL plate
AKR1           PDA200E 120m2 Waiting room loop kit
               c/w PDA200E amplifier, APL plate
AKU1           PDA200E 120m2 Retail unit loop kit
               c/w PDA200E amplifier, AML lectern mic, APJ plate
AKW1           PDA200E 120m2 Place of worship loop kit 1
               c/w PDA200E amplifier, AML lectern mic, APJ plate, APL plate
AKW2/L         PDA200E 120m2 Place of worship loop kit 2(lavalier mic. version)
               c/w PDA200E amplifier, AMR/LA lavalier radio mic, APQM plate, 2 x APXM plate
AKW2/H         PDA200E 120m2 Place of worship loop kit 2 (handheld mic. version)
               c/w PDA200E amplifier, AMR/HA handheld radio mic, APQM plate, 2 x APXM plate
AKH1/L         PDA200E 120m2 Health and fitness club loop kit (lavalier mic. version)
               c/w PDA200E amplifier, AMR/LA lavalier radio mic, APQM plate, APL plate
AKH1/H         PDA200E 120m2 Health and fitness club loop kit (handheld mic. version)
               c/w PDA200E amplifier, AMR/HA handheld radio mic, APQM plate, APL plate

PRO-RANGE (200m2 to 900m2) INDUCTIONLOOP AMPLIFIERS
PDA200/2       200m2 free standing induction loop amplifier
PDA500/2       500m2 free standing induction loop amplifier
PDA1000/2      900m2 free standing induction loop amplifier
PDA/RM         19” rack mount kit for PDA Pro-Range amplifier
PDA/WM         Wall mount kit for PDA Pro-Range amplifier

OUTREACH PLATE AUDIO INPUT EXTENSION SYSTEM
CAN BE USED TO INCREASE THE NUMBER OF AUDIO INPUTS ON AN INDUCTION LOOP SYSTEM*
*The ML1, PDA102, PDA200E and PDA Pro-Range amplifiers all have Outreach connection sockets. A separate 12V
PSU may be required when connecting outreach plates to other amplifiers. Plates should be wired using Belden 8723
audio cable.
APJ            3.5mm mono jack plate, for connection of AMT, AMH, AML or AMD microphones
APL            Line level audio plate, for connection of APS SCART lead/other line level audio feeds
APQM           6.35mm stereo jack plate, for connection of AMR/L &AMR/H radio microphone kit
APQL           6.35mm stereo jack plate, for connection of line level feeds from mixing desks, etc
APXM           XLR mic level plate, for connection of AMP microphone
APXL           XLR line level plate, for connection of line level feeds from mixing desks, etc
APM            Omni-directional plated microphone, for wall/ceiling/desk mounting
API            AFILS active indicator light
APS            SCART to double phono lead (for use with APL plate)

PDA RANGE MICROPHONES
APM            Omni-directional plated microphone, for wall/ceiling/desk mounting
               For direct connection to ML1, DL50, VL1, PDA102, PDA200E, PDA Pro-Range or an outreach chain
AMT            Tie/desk microphone for ML1, DL50, VL1, PDA102, PDA200E, PL1, PDA Pro-Range or APJ plate
AMH            Handheld microphone for ML1, DL50, VL1, PDA102, PDA200E, PL1, PDA Pro-Range or APJ plate
AML            Lectern microphone for ML1, DL50, VL1, PDA102, PDA200E, PL1, PDA Pro-Range or APJ plate
AMLS           Lectern microphone (short stemmed version of AML)

                      A GUIDE TO AUDIO-FREQUENCY INDUCTION LOOP SYSTEMS • PAGE 30
AMD            Desktop microphone for ML1, DL50, VL1, PDA102, PDA200E, PL1, PDA Pro-Range or APJ plate
AMDS           Desktop microphone (short stemmed version of AMD)
AMP            Professional handheld mic. for PDA200E or APXM outreach plate, requires AXLR lead
AMR/LA         Lavalier radio mic. (173.8 KHz) c/w Rx, Tx, psu. for PDA200E or APQM outreach plate
AMR/LB         Lavalier radio mic. (174.6 KHz) c/w Rx, Tx, psu. for PDA200E or APQM outreach plate
AMR/LC         Lavalier radio mic. (175.0 KHz) c/w Rx, Tx, psu. for PDA200E or APQM outreach plate
AMR/HA         Handheld radio mic. (173.8 KHz) c/w Rx, Tx, psu. for PDA200E or APQM outreach plate
AMR/HB         Handheld radio mic. (174.6 KHz) c/w Rx, Tx, psu. for PDA200E or APQM outreach plate
AMR/HC         Handheld radio mic. (175.0 KHz) c/w Rx, Tx, psu. for PDA200E or APQM outreach plate
PRO45          Hanging ambient microphone for PDAPro-Range or APXM plate

INDUCTION LOOP TEST EQUIPMENT
RXTI2          Induction loop test receiver requires 2 x AAA batteries & walkman type headphones
PNGN           Pink noise generator requires 1 x PP3 battery and AL1, AL2 or AL3 connection lead
AHHM           FoSmeter magnetic field strength meter - requires 1 x PP3 battery
AMPN           FoSmeter+ combined pink noise generator & magnetic field strength meter
               requires 1 x PP3 battery and AL1, AL2 or AL3 connection lead
AHHM/H         FoSmeter H combined magnetic field strength meter & loop listener
               requires 1 x PP3 battery & 32 Ohm headphones such as our HEAD1 headphones
HEAD1          32 Ohm headphones for use with AHHM/H
AL1            3.5mm jack to 3.5mm jack lead (connects PNGN to APJ outreach plate)
AL2            3.5mm jack to double phono lead (connects PNGN to APL outreach plate or DL50)
AL3            3.5mm jack to pre-cut bare ended lead

Loop cable is included in all ML1/K, VL1/B1, VL1/B2 DL50/K and PDA102 range induction loop kits. For PDA200E &
AK Range kits we recommend LOOP2/W cable. For other PDA range loop amplifiers, call our technical dept. for advice.

INDUCTION LOOP CABLE & MISCELLANEOUS OTHER AFILS ANCILLARIES
LOOP1/W        100m x 0.5mm2 single core white loop cable (for black cable order LOOP1/B)
LOOP2/W        100m x 1.0mm2 single core white loop cable (for black cable order LOOP2/B)
LOOP3/W        100m x 1.5mm2 single core white loop cable (for black cable order LOOP3/B)
LOOP4/W        100m x 2.5mm2 single corewhite loop cable (for black cable order LOOP4/B)
FLAT1005       100m x 0.5mm2 insulated copper tape (flat loop cable for under carpets)
FLAT2005       100m x 1.0 mm2 insulated copper tape (flat loop cable for under carpets)
FLAT3005       100m x 1.5mm2 insulated copper tape (flat loop cable for under carpets)
TAPE           50m white synthetic fibre tape (used to protect flat loop cable)
BELDEN/10      10m Belden 8723 four core screened cable for use with outreach plates
BELDEN/25      25m Belden 8723 four corescreened cable for use with outreach plates
APT            Loop connector plate (for the termination of induction loop cable)
AXLR           XLRto XLRlead (used to connect AMPmic to APXM outreach plate)
LEST           100V line (i.e PA system output) to 0db (775mV line level) convertor
APPS           Overspill reduction phase shifter
TEAR10         Pack of 10 self-adhesive ‘induction loop fitted’ stickers


                       A GUIDE TO AUDIO-FREQUENCY INDUCTION LOOP SYSTEMS • PAGE 31
                        C-TEC, Stephens Way, Wigan WN3 6PH. United Kingdom.
                        UK Sales:          Tel: 01942 322744
                                           Fax: 01942 829867
                                           E-Mail: sales@c-tec.co.uk
                        European Sales:    Tel: +44 1942 322744
                                           Fax: +44 1942 829867
                                           E-Mail: eu.exports@c-tec.co.uk
                        Export Sales:      Tel: +44 161 257 2541
                                           Fax: +44 161 225 8817
                                           E-Mail: xportsales@xportsales.com
                                           Website: www.c-tec.co.uk




 Approved Document No. DLU6560501 Rev 1. E&OE. No responsibility can be accepted by the
manufacturer or distributors of the PDA Range of audio frequency induction loop equipment for any
misinterpretation of an instruction or guidance note or for the compliance of the system as a whole.